Genetic algorithm rheological equations for cement paste

Abstract

The rheological behaviour of cement pastes incorporating superplasticisers is influenced by the ambient temperature and mixing time; which is critical for hot weather concreting. Rheological parameters including yield stress and plastic viscosity of cement pastes with a water/cement ratio of 0·38 and incorporating polycarboxylate-, melamine sulfonate-, and naphthalene sulfonate-based superplasticisers were measured as a function of the superplasticiser dosage and temperature (22–45°C) over 20 to 110 min from the time of mixing, with 30 min between successive measurements. The rheological tests were conducted using an advanced shear-stress/shear-strain controlled rheometer. Test results indicate that the yield stress and plastic viscosity of cement paste vary in a linear fashion with the elapsed time, whereas their variations with the temperature and superplasticiser dosage follow power and inverse power functions, respectively. In this study, curves showing shear stress plotted against shear rate for cement pastes incorporating the various superplasticisers at different ambient temperatures and mixing times were predicted using genetic algorithms. Rheological equations were then derived from these curves using the Bingham model and employed to predict the yield stress and plastic viscosity of cement pastes. A sensitivity study was performed to evaluate the effects of mixing time, ambient temperature, and superplasticiser dosage on the calculated yield stress and plastic viscosity. It was shown that the computed yield stress and plastic viscosity values compared well with corresponding experimental data